| OCR Text |
Show release in a combustion system. The initial applicability is to clean gaseous and vaporizable liquid fuels as a premixed fuel and air stream must be presented to the catalyst. Oxidation of the fuel through both heterogeneous surface reactions and homogeneous gas phase reactions occurs within the channels of the catalyst bed at essentially adiabatic temperature. Complete combustion can be achieved at very short residence time and with very high volumetric heat release rates. The two apparent limits are (a) the temperature at which catalyst degradation becomes significant, and (b) the well known kinetic threshold temperature above which the rate of thermal N0X formation becomes significant. Therefore the application of the technology to stationary combustion sources requires new system designs to achieve long life and high thermal efficiency. The graded cell catalyst has been developed during the program and patented. This concept uses large cells at the inlet end of the catalyst monolith to maintain heterogeneous ignition at very high fuel throughput (space velocity) with progressively smaller cells to complete the fuel oxidation. This concept has been tested versus a conventional straight cell catalyst of the same formulation. The graded cell catalyst achieved three times the volumetric energy release of the straight cell and had a much more uniform axial temperature profile. In addition, other versions of the graded cell have shown extremely high heat release capability (> 10** Btu/hr/ft^/ATM) and low thermal N0X (< 50 ppm at 1700°C). The graded cell catalyst appears to be a major improvement in combustion catalyst technology. There has also been significant progress in the development of systems for application of catalytic combustion to boilers burning nitrogen containing fuels. A catalytic staged combustor has been designed and tested, using the configuration shown in Figure 16. The first stage bed is run fuel rich to partially oxidize the fuel and to promote formation of N2 from fuel nitrogen compounds. Heat is removed between stages to reduce the adiabatic temperature in the second stage. Then the balance of the air is added and the fuel oxidation is completed in the second stage catalyst. This configuration allows the overall system to operate at minimum excess air for high efficiency without exceeding the allowable temperature in either catalyst bed. The conversion of 3-45 45 |
